Equipment and supplies Design and construction 331 Air conditioning 200 Wireless communication systems 164 Maintenance and repair 160 Ventilation 133 Heating 126 Radio circuits 81 Radio 76 Microcomputers 73 Testing 69 Telecommunication 67 Purification 66 Sound 66 Automobiles 61 Optical communications 54 Automatic control 50 Recording and reproducing 49 Air 45 Upgrading 45 Chemical plants 40 Fiber optics 39 Electric power systems 34 Materials 34 Chemical processes 31 Electric power distribution 31 Integrated circuits 31 Engineering 30 Transmitter-receivers 29 Digital techniques 28